Sri Lanka Elections: Rajapaksa Seeks Comeback
Mr Rajapaksa had lost the presidency in a snap election in January to his former Health Minister, Maithripala Sirisena.
Four people had died in violent incidents during the campaign, although, monitors said that there had been less violence compared to previous years.
With 15 million people eligible to cast their vote, the exercise would end at 4:00pm and results would be released on Tuesday.
Mr Rajapaksa was hailed a warrior king for defeating the Tamil Tiger separatists to end a nearly 26-year civil war.
However, he was accused of using his popularity to take control of parliament, the courts, armed forces and all government institutions.
He was also accused of widespread human rights abuses and suppressing freedoms.
Mr Rajapaksa sought an extended period of rule after abolishing a two-term limit for presidents when he lost in his attempt to win a third term.
His main rival is the sitting Prime Minister, Ranil Wickremesinghe, a two-time Prime Minister.